TCP_STATES = { # /usr/src/linux/include/net/tcp_states.h
  "00" => "UNKNOWN",
  "FF" => "UNKNOWN",
  "01" => "ESTABLISHED",
  "02" => "SYN_SENT",
  "03" => "SYN_RECV",
  "04" => "FIN_WAIT1",
  "05" => "FIN_WAIT2",
  "06" => "TIME_WAIT",
  "07" => "CLOSE",
  "08" => "CLOSE_WAIT",
  "09" => "LAST_ACK",
  "0A" => "LISTEN",
  "0B" => "CLOSING",
  "0C" => "NEW_SYN_RECV"
}

module Etc
  def self.getpwuid(uid)
    File.read_lines("/etc/passwd").each_with_index do |line, i|
      entry = line.split(":", remove_empty: false)
      return entry[0] if entry[2] == uid
    end
  end
end

def decode_addr(addr)
  ip, port = addr.split(":", remove_empty: true)
  ip = ip.scan(/.{2}/).reverse_each.join('.'){ |x| x[0].to_i(16) }
  port = port.to_i(16).to_s
  "#{ip}:#{port}"
end

puts "local address".ljust(22) + "remote address".ljust(22) + "state".ljust(12) + "username (uid)"
File.read_lines("/proc/net/tcp").each_with_index do |line, i|
  entry = line.split(" ", remove_empty: true)
  unless i == 0 # skip headers
    laddr = decode_addr(entry[1])
    raddr = decode_addr(entry[2])
    state = TCP_STATES[entry[3]]
    uid = entry[7]
    uname = Etc.getpwuid(uid)
    puts "#{laddr.ljust(22)}#{raddr.ljust(22)}#{state.ljust(12)}#{uname} (#{uid})"
  end
end